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[209.132.183.28]) by mx.google.com with ESMTPS id w2si19196593qkf.216.2019.07.19.07.09.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Jul 2019 07:09:08 -0700 (PDT) Received-SPF: pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=longman@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0616181F2F; Fri, 19 Jul 2019 14:09:08 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-160.bos.redhat.com [10.18.17.160]) by smtp.corp.redhat.com (Postfix) with ESMTP id D59842FC5B; Fri, 19 Jul 2019 14:09:06 +0000 (UTC) Subject: Re: [PATCH v2 1/2] mm, slab: Extend slab/shrink to shrink all memcg caches To: Michal Hocko Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Roman Gushchin , Johannes Weiner , Shakeel Butt , Vladimir Davydov References: <20190717202413.13237-1-longman@redhat.com> <20190717202413.13237-2-longman@redhat.com> <20190719062052.GK30461@dhcp22.suse.cz> From: Waiman Long Organization: Red Hat Message-ID: Date: Fri, 19 Jul 2019 10:09:06 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190719062052.GK30461@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Fri, 19 Jul 2019 14:09:08 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 7/19/19 2:20 AM, Michal Hocko wrote: > On Wed 17-07-19 16:24:12, Waiman Long wrote: >> Currently, a value of '1" is written to /sys/kernel/slab//shrink >> file to shrink the slab by flushing out all the per-cpu slabs and free >> slabs in partial lists. This can be useful to squeeze out a bit more memory >> under extreme condition as well as making the active object counts in >> /proc/slabinfo more accurate. >> >> This usually applies only to the root caches, as the SLUB_MEMCG_SYSFS_ON >> option is usually not enabled and "slub_memcg_sysfs=1" not set. Even >> if memcg sysfs is turned on, it is too cumbersome and impractical to >> manage all those per-memcg sysfs files in a real production system. >> >> So there is no practical way to shrink memcg caches. Fix this by >> enabling a proper write to the shrink sysfs file of the root cache >> to scan all the available memcg caches and shrink them as well. For a >> non-root memcg cache (when SLUB_MEMCG_SYSFS_ON or slub_memcg_sysfs is >> on), only that cache will be shrunk when written. > I would mention that memcg unawareness was an overlook more than > anything else. The interface is intended to shrink all pcp data of the > cache. The fact that we are using per-memcg internal caches is an > implementation detail. > >> On a 2-socket 64-core 256-thread arm64 system with 64k page after >> a parallel kernel build, the the amount of memory occupied by slabs >> before shrinking slabs were: >> >> # grep task_struct /proc/slabinfo >> task_struct 53137 53192 4288 61 4 : tunables 0 0 >> 0 : slabdata 872 872 0 >> # grep "^S[lRU]" /proc/meminfo >> Slab: 3936832 kB >> SReclaimable: 399104 kB >> SUnreclaim: 3537728 kB >> >> After shrinking slabs: >> >> # grep "^S[lRU]" /proc/meminfo >> Slab: 1356288 kB >> SReclaimable: 263296 kB >> SUnreclaim: 1092992 kB >> # grep task_struct /proc/slabinfo >> task_struct 2764 6832 4288 61 4 : tunables 0 0 >> 0 : slabdata 112 112 0 > Now that you are touching the documentation I would just add a note that > shrinking might be expensive and block other slab operations so it > should be used with some care. > Good point. I will update the patch to include such a note in the documentation. Thanks, Longman